[minitoo]

hey guys,
I'll bet "tagged" means ticketed to you and thats why you mention the legality thing? Actually I meant "tagged" to mean a slap on the butt as in the child's game of tag. Don't know all about the laws on flashing brake lights to indicate you are slowing but I'm sure they are probably different wherever we are. My intent was just to remind folks that a close follower, lost in the ozone, may not be aware of the fact that you are slowing and your car gets hit from behind. They may be at fault but its sort of the deal where you are "dead right" but you still get a damaged car or even hurt. There are an awfully lot of uninvolved drivers out there and we aren't about to change them. And I gotta confess to stepping the gears down coming into a favorite curve myself....increased wear be damned!

[Yellow/Black OneD]

Quote: Originally Posted by Tigger, Eeyore & Roo

Nice idea and I appreciate what you are trying to do, but you are actually using MORE fuel doing this!!

If you drive down hill in neutral the engine uses fuel just to keep idling. If you run down hill using engine braking then the fuel supply to the engine in any modern car is shut off and the only thing keeping the engine turning over is the road wheels rotating.

The end result is that fuel is used in neutral, no fuel used when left in gear! It surprised me when I found this out.

Tigger.

This is very correct. You only have to check your OBC out to realise this!! 99.9mpg when in gear with no throttle, e.g going down hill!! VW's actually show ---- when doing that and about 89mpg when in neutral! So you do use fuel in neutral but not a drop when in gear with no throttle.

[nonsequitur]

Quote: Originally Posted by Yellow/Black OneD

So you do use fuel in neutral but not a drop when in gear with no throttle.

Somebody needs to research this one.

The engine does not turn off in throttle off situations (downhill example), and the road wheels do not keeping the engine rotating.

Fuel is being consumed, just not near as much.

[Kodak]

Quote: Originally Posted by nonsequitur

Somebody needs to research this one.

The engine does not turn off in throttle off situations (downhill example), and the road wheels do not keeping the engine rotating.

Fuel is being consumed, just not near as much.

'Tis true,

Absolutely NO fuel is being used on modern cars as the fuel is cut off. They are intelligent enough to know when it is happening... In neutral a (very) small amount is used to keep the car idling.

Also heard Clarkson on Top Gear mention it.


Suprised me when I first heard it, as I used to coast in neutral to traffic lights..etc in my old car (Renault Clio 16v) to "make up for" the fuel I used when flooring it...
Floored it much more than coasting, so made little difference anyway.


Stopped doing it in the MINI....

[jazmini]

Quote: Originally Posted by am0eba

jazmini - I've never heard of anyone getting ticketed for slowing down without using their brakes either, but at least in Massachusetts and California, the law states that drivers MUST signal when slowing down or stopping. If you're using the brakes and they are functioning properly, the brake lights automatically do this signalling for you. If you use the handbrake or compression braking, you are obliged to signal somehow, whether by tapping the brake pedal lightly, or using the appropriate hand signal. (Remember those?) ...... I guess my point (yeeesss?) is that the driver should feel obliged to consider tthe vehicles and drivers around him at all times and act accordingly...
_Dave_

Dave -- Thanks for the update -- I'll try to remember to tap my brakes while downshifting when someone is following close. Yes, I do remember hand signals. People used them with the older cars. Your arm stuck out the window with palm flat pointing downward signifies slowing down. You could also give hand signals for left and right turns. I used them with my motorcycles without turn signals, I just never used them for slowing down while downshifting. I can see it's a safe thing to do.

[nonsequitur]

Quote: Originally Posted by Kodak

Absolutely NO fuel is being used on modern cars as the fuel is cut off.

Quote: Originally Posted by Yellow/Black OneD

So you do use fuel in neutral but not a drop when in gear with no throttle.

Quote: Originally Posted by Tigger, Eeyore & Roo

If you run down hill using engine braking then the fuel supply to the engine in any modern car is shut off and the only thing keeping the engine turning over is the road wheels rotating.

These statements are not correct, guys.

Fuel is being used, the engine is running as the result of combustion in the cylinders, although in modern cars it is a much smaller amount than was the case in earlier years. What DOES happen is that fuel control is cut off from the throttle, taken over by the DME, and then metered very carefully to the motor based on ambient air conditions (pressure, temperature, etc) for maximum fuel economy.

A simple test is the tachometer, which is connected to the electronics (in modern cars) of the engine. It drops to an idle level, but it's still running.

Confirmed with BMW Group, 1-866-ASK-MINI, and a couple of dealers.

[A.Naimoli]

I don't downshift when approaching a stop sign or light. I usually put it in neutral, coast, and brake. In fact, I've seen some signs on a local highway saying "excessing engine braking prohibited."

How does the car behind you know that you're downshifting? Doesn't this sometimes cause rear car collisions?

[am0eba]

Quote: Originally Posted by A.Naimoli

... In fact, I've seen some signs on a local highway saying "excessing engine braking prohibited." ...

This is a noise-abatement issue. The restriction on engine-braking is to minimize the occurrance of the
BRA AA AA AAA AAAA KKK KKK KKK KKKK !!!
Noise that is generated when heavy trucks engage their "Jake Brake". (Note: Jake Brake is a registered trademark in the US, and is only used here as a generic term for engine compression braking systems, similar to the use of "Xerox" for photocopy, and "Kleenex" for paper tissue.)

_Dave_

[JTC]

Quote: Originally Posted by am0eba

Noise that is generated when heavy trucks engage their "Jake Brake".
_Dave_

i think they call it compression brakin in australia...see them around the motorways


i lvoe engine braking....does anyone know if usin the brakes also use fuel??...that is required compression to the brake disc?

[mataku]

wow.. such a long discusssion, but seems to be very little consensus.

I have a CVT and use engine braking almost all the time in the city. Before I used to shift to neutral and slow down with my brakes, but after doing this for a bit, I started feeling like the transmission was getting very loose. This seems to be because of the constant shifting that happens.

Regarding all these issues, what's the best way to slow down in a CVT, a)engine braking, b)neutral and brake, or c)just brakes?

[Paul!]

Quote: Originally Posted by mataku

wow.. such a long discusssion, but seems to be very little consensus.

I have a CVT and use engine braking almost all the time in the city. Before I used to shift to neutral and slow down with my brakes, but after doing this for a bit, I started feeling like the transmission was getting very loose. This seems to be because of the constant shifting that happens....

Hmm, interesting problem. I had a Nissan Micra with a CVT back when I was in England, and according to how Nissan claims the trannsmission worked, every time your foot wasn't on the gas, the car was in neutral. And if I understand correctly, that's how the MINI CVT should operate, if it wasn't for BMW 'forcing' it via programming to stay in gear, hence our cars 'creep'.

Anyway, I don't think that neutral/brake slowing should damage the CVT, in my unqualified opinion.

-Paul!

[mataku]

I wonder if the neutral/brake thing does damage. Not from the action itself, but from the constant action that's happening. I mean, if I want to slow down, I used to shift from the steptronic drive all the way to neutral, then if the traffic gets going before i stop I would shift back to the steptronic from neutral.

I don't know, I've just had my transmission cable tigtened and it felt really solid, but after doing the whole neutral thing, it feels a bit loose again. Also, when doing the process it just feels bad.

[nonsequitur]

Quote: Originally Posted by mataku

Regarding all these issues, what's the best way to slow down in a CVT, a) engine braking, b) neutral and brake, or c) just brakes?

The car, engine, gearbox, and drivetrain was designed for use in an expected and conventional way. That tips the logics toward a) and c), not b).

Shifting to Neutral is a physical change on the gearbox, the other combinations we've talked about are expressed through programming.

I don't see what switching to Neutral gains in performance, predicable reaction, mechanical wear, or fuel savings?

When driving in more stressed situations (like the track), the key points are smooth inputs (steering, brake, gas, with both hands on the steering wheel), a proper line through the corners, and eyes up (to see what's going to happen before it does). These suggestions apply here too.

The "best way" is always the one that 1) minimizes stress on the components (even a top fuel drag racer launch), 2) keeps the car balanced (no jerky changes), and 3) retains momentum (ideas like slowing smoothly and only to the speed required, applying some throttle in the corner, etc). I'd recommend not using Neutral except when stopped; at a very long light maybe, in very heavy traffic maybe, ... On this point, drive it like you would a Manual!

[mataku]

smooth... i like that. However, it also seems like the engine braking puts stress on the engine itself, making me think simply braking is the best, unfortunately also the least fun.

one note though, it seems that I get better gas mileage with engine braking. over the last two weeks, everytime I get in the car and start driving I would see my range go up as I drove for a certain time. Say it would go from 191-197-192, i take short trips. HOwever, today when I just drove like a normal automatic, the gas mileage started at 188 and kept declining to 181. Halfway to my destination I drove with the engine braking and it went up from 181- 184. note: I only shift at 2000 rpm and it goes up to only 3000 rpms.

so, is the computer just wrong or being tricked, or am i actually getting better mileage?

[nonsequitur]

Quote: Originally Posted by mataku

... engine braking puts stress on the engine itself ...

I'd say "Definitely not." In fact, I'd say that it helps engine longevity.
Any contrary opinion?

[mataku]

Quote: Originally Posted by nonsequitur

I'd say "Definitely not." In fact, I'd say that it helps engine longevity.
Any contrary opinion?

I'm going based on the fact that someone mentioned, in order to stop, the friction has to come from somewhere. Therefore with engine braking, since it's not coming from the normal brakes it's coming from somewhere in the drivetrain.

Maybe someone could explain mechanically what happens when you engine brake and then what that means in terms of the CVT engine?

still wondering about the fuel economy thing though.

[ToplessRed]

Thinking through the physics, I supose it's possible for engine braking to be more fuel efficient. Think about why highway MPG is so much better than city MPG. On the highway, you are driving faster so you are fighting against higher kinetic friction (slows objects down). However in city driving, there's a lot of stop-and-go so you're constantly encountering static friction (keeps non-moving objects from moving). At least normal driving speeds of cars, static friction tends to be much stronger than kinetic friction.

With friction in mind, let's now compare engine braking versus regular braking. Step on the brakes, friction slows you down of course but what also happens is your engine RPM tends to slowly drift down. When it's time to speed up again, you step on the gas and once against you are fighting against the initial lumpsum friction force. When you downshift, your engine spins up faster -- however, you aren't spending fuel to do this as it's the inertia of your car that's responsible. So after you hang your corner and you want to speed up again, you don't have to pay the initial friction penalty as Newtonian physics has given you higher RPMs for free.

Note, this example only works if you don't make a complete stop. In addition, I'm just making wild guesses from what the physics courses I took in college 10 years ago.

[nonsequitur]

Quote: Originally Posted by ToplessRed

... step on the gas...

That's it: Throttle position = fuel economy experience!

On the road, throttle is steady and the road is flying beneath (higher "mileage");
in town, the throttle is in near constant motion,
acceleration uses much more fuel per unit of distance,
and sitting at a stop light = 0 mpg.

On the road, there's a balance between road distance covered and fuel use;
in town, you're just not going very far per unit of time (lower "mileage").

[Dutchy]

Quote: Originally Posted by nonsequitur

That's it: Throttle position = fuel economy experience!

On the road, throttle is steady and the road is flying beneath (higher "mileage");
in town, the throttle is in near constant in motion,
acceleration uses much more fuel per unit of distance,
and sitting at a stop light = 0 mpg.

On the road, there's a balance between road distance covered and fuel use;
in town, you're just not going very far per unit of time (lower "mileage").

Your theory of being stopped at a traffic light equalling 0 mpg is good, but try telling my OBC that, and it will laugh in your face. In my car when stopped at a set of lights, the OBC will keep raising the L/100kms figure ie using more fuel, until I take off and get to a steady speed. If I am at highway speeds and take my foot off the accelerator ie down a hill, the OBC will read 0 L/100kms (if I reset the reading before the hill).

[nonsequitur]

Quote: Originally Posted by Dutchy

In my car when stopped at a set of lights, the OBC will keep raising the L/100kms figure ie using more fuel, until I take off and get to a steady speed. If I am at highway speeds and take my foot off the accelerator ie down a hill, the OBC will read 0 L/100kms (if I reset the reading before the hill).

This has been bothering me... so today I was able to try several experiments with the Cooper CVT because my wife is out of town (she's "acquired" the '02 as "hers" for work and the commute, over my consistent protests).

Cruising at highway speeds.
Reset the computer MPG and MPH.
The OBC "jumps" to a new number, and then settles into an average that matches the speedometer (2-3% optimistic). This seems completely as expected. The "sweet spot" still appears to be somewhere around 57mph (from the OBC) for the best ave mpg.

Stopped on a flat surface, engine running, I.
Reset the computer MPG and MPH (both read "- - -".)
The OBC does absolutely nothing. No change in MPG or MPH.

Stopped on a flat surface, engine running, II.
Don't reset the computer for MPG or MPH (retain existing numbers in memory).
Ave MPG steadily drops down in 0.1 Mile/Gal steps.
Ave MPH steadily decreases in approximately 0.4Mile/Hour steps (this is dependent on hour much data is in memory).

Headed steep downhill, throttle off.
Reset the computer MPG and MPH at the top of the hill.
Ave MPG pegs at 99.9mpg, and Ave MPH quickly crawls up to the actual number.

Headed steep downhill, throttle off.
Don't reset the computer for MPG or MPH (retain existing numbers in memory).
Ave MPG starts increasing (fast or slow, depending on how long data has been accumulating in the OBC; recent reset = fast; lots of previous time = slow).